CODEWITHSUNDEEP
jsonscalajackson
Havnar
Havnar

Reputation: 2638

Merge multiple JsonNodes into an array with Jackson

I need to write some appender method that adds "JsonNode" objects together. In the end, this would run recursively over a few hundreds of iterations. Eventually I would convert it to an Avro object. So apart from "just getting it to work" I would also want to keep memory consumption into consideration.

A simplified example below:

  val s1 = """{"condition": "yes",
    "id": "file",
    "value": "File" }"""

  val s2 = """{"condition": "no",
    "id": "file2",
    "value": "File2" }"""

  val mapper = new ObjectMapper()

  val obj1: JsonNode = mapper.readTree(s1)
  val obj2: JsonNode = mapper.readTree(s2)

  // the following doesn't work obviously, but that's what I'm trying to do
  val result = obj1 + obj2
  println(result.toString)

the desired output would be:

[{"condition": "yes",
    "id": "file",
    "value": "File" },
 {"condition": "no",
    "id": "file2",
    "value": "File2" }]

I've been fiddling around with a few options, but I can't seem to get an easy append to work. Unless of course I go the "string" route, but that's not as clean as I would like it to be. (append s1 and s2 seperated by a , and wrap it in [] brackets)

Upvotes: 2

Views: 4194

Answers (1)

Thomas Fritsch
Thomas Fritsch

Reputation: 10127

As @yokomizor already commented, you need to build an ArrayNode with the two elements obj1 and obj2:

val result: ArrayNode = mapper.createArrayNode()
result.add(obj1)
result.add(obj2)

or even simpler:

val result: ArrayNode = mapper.createArrayNode().add(obj1).add(obj2)

The additional memory foot-print of this is as small as it can be, because the internal implementation of ArrayNode simply has a private List<JsonNode> _children, and you have the JsonNodes already in memory anyway.

Upvotes: 2

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